Sonoelastography is an ultrasound imaging technique where low amplitude, and low frequency shear waves are propagated through organs and tissue while real time Doppler techniques are used to image the resulting vibration pattern. Hard lesions such as tumours in the presence of soft tissue, such in breast cancer, will have reduced vibration amplitude, which is readily imaged by ultrasonic means.
Malignant tumours manifest themselves by way of pathological changes such as variation in the tissue's mechanical stiffness, which can be detected by a reduction in strain as compared to the surrounding soft tissue.
An existing technique known as “elastography” is used in breast tumour diagnosis whereby ultrasonic echo data is collected before and after a slight “compression” of the tissue. Comparisons can be made between normal and pathologically affected tissue by gathers information on the static elastic properties of the tissue before and during compression. The differing elastic properties between a benign and malignant tumour can be distinguished by an ultrasound echo detection device.
In yet another area of research, it has been documented that a rapidly changing strain or vibration applied to the tissue will result in more defined differences between healthy and pathological tissue. To better distinguish variations in tissue elastic properties, the vibrational frequency response is dependant upon the induced excitation frequency and the amplitude of the vibration source.
Variations in tissue motion can be detected by frequency shifts in ultrasonic echoes and imaged using conventional 2D ultrasound scanners and Doppler ultrasound scanners; a method commonly used to highlight blood flow.
The apparatus of the present disclosure also has application in treatment of osteoporosis. The skeletal bone structure of a human is considered to be a frameworks of levers upon which muscles are attach to enable movement of the whole body. The skeletal bones are subjected to many varying vibrations due to locomotion, bodily functions, stress, strain and also due to the anchorage of muscle fibres and tendons which are continuously vibrating at different frequencies depending upon the strain applied to them. Bones are subjected to compression influences and vibration during the act of walking, running and jumping and these vibrations reverberate up through the skeletal structure passing through the whole body.
It is well documented that bone metabolism is responsive and triggered by mechanical strain. Mechanical loads can be applied through weight bearing exercise or they can be applied by mechanical external sources to the body to cause in vivo deformations of the bone. It is this deformation that signals the bone cells to remodel (rebuild or adapt) the skeletal structure to accommodate the strain applied. This biological phenomenon has long been recognised by physicians for the prevention and treatment of the bone loss condition known as osteoporosis.
In the 1890's Julius Wolff a German anatomist, claimed that bone structure could adapt in response to a changing mechanical environment and that the orientation of trabeculae could be changed if there was a change in mechanical stress directions. The biological response of bone to mechanical loading is a complex function and differs according to the individual, the magnitude and the pattern and “direction of the stress” applied. Dynamic mechanical loading leads to interstitial fluid flow within the fluid spaces of bone which plays an important role in providing hydrostatic shear pressure to activate the bone cells into remodelling action.
Traditional vibration devices are in the form of one-dimensional acoustic speaker type transducers whereby the vibration is delivered in the form of a linear stroke in the “z” or vertical axis. This form of vibration transducer can vary the frequency output but cannot offer any variation to the mono dimensional amplitude. When used in sonoelastography, the vibration source of this type is required to be repositioned many times during scanning to improve the quality of the 3D mapping reconstruction and to reduce the shadowing effect. Another disadvantage of this form of vibration is that it can generate modal patterns which can make image interpretation difficult.
In treatment of osteoporosis, prior art stimulating devices consist of transducer type, vertically moving platforms, which the patient either stands or sits upon. This method applies a compression load to the bones which is converted to a measure of micro-strains by determining the change in the bones length divided by the original bone length. This compression load must be of a significant force to reflect a change in the length of a bones due to the bone matrix being far stronger in compression than in shear. These prior art transducer methods of applying a vertical compressive stress to the skeletal structure have limited success in applying mechanical stimulus to the wider range of bones such as ribs and short plate like pelvic and hip bones to affect a change in bone rebuilding. With this form of shock loading the joints and cartilages must also endure the stress and further transmit the vibration along to the next set of bones for them to benefit from the stress stimulus.
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